Currently, the law allows abortion to be performed only to save a mother's life or to preserve her physical or mental health. The procedure must be approved by two doctors or consultants.

If the Bill becomes law, when a woman is more than 20 weeks pregnant, a health practitioner would need to determine the abortion is appropriate with regard to the woman's physical and mental health.

Mr Little said the bill would modernise New Zealand's abortion laws, bringing them into line with laws in other developed countries.

"Abortion is the only medical procedure that is still a crime in New Zealand. It's time for this to change.

"Safe abortion should be treated and regulated as a health issue; a woman has the right to choose what happens to her body.

"Oversight of abortion services would be transferred from the Abortion Supervisory Committee to the Ministry of Health", Mr Little said.

Prime Minister Jacinda Ardern said she senses the vote results "will be close".

The Bill would:

Remove any statutory test on the health practitioner for a woman who is not more than 20 weeks pregnant.

For a woman who is more than 20 weeks pregnant, require the health practitioner to reasonably believe the abortion is appropriate with regard to the pregnant woman's physical and mental health, and well-being.

Ensure that health practitioners advise women of the availability of counselling services if they are considering an abortion or have had an abortion, although counselling will not be mandatory.

Ensure that a woman can self-refer to an abortion service provider.

Enable a regulation-making power to set up safe areas around specific abortion facilities, on a case-by-case basis.

Ensure that practitioners who object to providing services on the grounds of conscience must inform the pregnant women about their objection, and that the woman can obtain the services elsewhere.

Retain the criminal offence for unqualified people who attempt to procure an abortion on a pregnant woman or supply the means for procuring an abortion.

Retain the criminal offence of killing an unborn child for any person who causes harm to a pregnant woman and in doing so causes the death of a fetus.

The Bill will be treated as a conscience issue, meaning MPs will be able to vote independently at each stage.